We have developed a water calorimeter which has the following immediate advantages (1) the dose is measured in the recommended medium of water; and (2) the calorimeter is simple in concept and operation. We have also developed a direct voltage-measurement technique using a digital voltmeter which has greatly simplified the monitoring of the calorimeter and made it possible to achieve digital data processing by a computer. The objective is to develop an instrument for the determination of absorbed dose. We intend to further develop a number of capabilities by means of: (1) a pulsed calorimeter to gain 25-fold increase in sensitivity by increasing the pulsed voltage for the same average heat consumption as that with the conventional DC technique; and (2) a mini-computer linkage for interactive operations and real-time data analysis. The goal is to construct a portable calorimeter for instant absorbed dose determination and to establish it as the absolute absorbed dose detector: 1) We intend to use this portable calorimeter for a variety of radiation beams Co-60 gamma rays, 4, 6 and 18 MV x-rays, and 12 and 20 MeV electron beams; 2) We intend to use the calorimeter for non-conventional beams; proton and neutron beams, where the dose discrepancies were reported to be as large as 10% among different dosimeters; 3) We intend to determine the heat defect of water by absorbed dose comparison between water and polystyrene-water calorimeters; 4) We intend to establish a standard data analysis method for a polystyrene-water calorimeter, which has a troublesome upward concave shape during post-irradiation drifts. If this program demonstrates the advantage of a high sensitivity pulsed calorimeter, it will provide an important step toward determining the absolute absorbed dose which is fundamental in radiation therapy.